Graphene, is an atomically thin two-dimensional (2D) sheet of covalently bonded carbon atoms arranged in a hexagonal, honeycomb-like pattern. Graphene exhibits spectacular mechanical properties, as, for example, a Young modulus that approaches 1 TPa and tensile strength that is an order of magnitude higher than that of the best steel, for the same sample thickness. The thickness of a graphene monolayer is 0.34 nm, thus for macroscopic application thousands of graphene layers would have to be stacked together, because, while the strength of single-layer graphene is outstanding, single-layer graphene is too thin for practical applications. Unfortunately, the weak van der Waals interlayer forces acting between consecutive graphene layers within the stack are responsible for the low shear strength of the stack.
Therefore, there is a need for controllably reinforcing the interlayer bonding in the multi-layer stack by incorporating covalent bonds between adjacent graphene layers with control over the number and spatial distribution of the interlayer bonds.